The conditional chunk defines the conditions under which other chunks should be used.
The conditional chunk in the DLS file format has the following structure.
| Byte sequence description | Length in bytes | Starts at byte in the chunk | Value |
| chunk ID | 4 | 0x00 | The ASCII character string "cld " (note the space) |
| size | various | 0x04 | The size of the chunk in number of bytes (unsigned integer) less 8 (less the size of "chunk ID" and the "size") |
| operations | various | 0x08 | A sequence of operations, as defined below |
Operations
An operation can have one of three forms.
- Operation code (unsigned two-byte value)
- Operation code (unsigned two-byte value), DLS ID (16-byte value; see DLS ID chunk (of a DLS file))
- Operation code (unsigned two-byte value), unsigned long (eight-byte integer)
Operation codes
The following are the operation codes.
| Operation code | Value | Interpretation (C code) |
| AND | 0x0001 | X & Y |
| OR | 0x0002 | X | Y |
| Exclusive OR | 0x0003 | X ^ Y |
| Add | 0x0004 | X + Y |
| Subtract | 0x0005 | X - Y |
| Multiply | 0x0006 | X * Y |
| Divide | 0x0007 | X / Y |
| Logical AND | 0x0008 | X && Y |
| Logical OR | 0x0009 | X || Y |
| Less than | 0x000A | X $lt; Y |
| Less than or equal to | 0x000B | X <= Y |
| Greater than | 0x000C | X > Y |
| Greater than or equal to | 0x000D | X >= Y |
| Equal | 0x000E | X == Y |
| NOT | 0x000F | ! X |
| Constant | 0x0010 | Z |
| Query | 0x0011 | Query DLS ID |
| Query supported | 0x0012 | Query supported DLS ID |
Operations are computed on a stack. Each time an operation is to be performed, the needed number of values are popped off the stack and the computed result is pushed back on the stack. X is the top value on the stack and Y is the previous value on the stack. Z is a constant that is pushed on the stack by a constant operation. When the operation is a query, then the device is queried and the returned value is pushed on the stack. When the operation is a query supported one, the device is queried and the return value, either TRUE or FALSE, is pushed on the stack.
FALSE is represented by binary zeroes, whereas TRUE is represented by binary ones. A non-zero value will also be interpreted as TRUE, which means that a NOT operation must take care to zero out bits.
The minimum supported stack that must be implemented by a device that supports DLS Level 2 is a stack of eight 32-bit values.
Placement of conditional chunks
The conditional chunk is a DLS Level 2 construct. A conditional chunk is not required in a DLS file.
The conditional chunk can be a top-level DLS chunk or can exist within a list. When in a conditional chunk is at the top of the DLS file and the device fails the conditions specified in this chunk, the whole DLS file is ignored, and an error code is returned to the application using the DLS file. When the conditional chunk is in a list and a device fails the corresponding conditions, then the list is ignored. When in a list, it is preferred that the conditional chunk is the first chunk in the list.
Standard DLS Level 2 queries
All DLS Level 2 devices must support the following queries.
| Query | UUID value | Return value |
| Supports DLS 1 | 0x178F2F27, 0xC364, 0x11D1, 0xA7, 0x60, 0x00, 0x00, 0xF8, 0x75, 0xAC, 0x12 | Returns TRUE if the device supports DLS Level 1 |
| Supports DLS 2 | 0xF14599E5, 0x4689, 0x11D2, 0xAF, 0xA6, 0x0, 0xAA, 0x0, 0x24, 0xD8, 0xB6 | Returns TRUE if the device supports DLS Level 2 |
| Manufacturer ID | 0xB03E1181, 0x8095, 0x11D2, 0xA1, 0xEF, 0x0, 0x60, 0x8, 0x33, 0xDB, 0xD8 | Returns the MIDI manufacturer ID in 24 bits |
| Product ID | 0xB03E1182, 0x8095, 0x11D2, 0xA1, 0xEF, 0x0, 0x60, 0x8, 0x33, 0xDB, 0xD8 | Returns the manufacturer specific product ID |
| General MIDI | 0x178F2F24, 0xC364, 0x11D1, 0xA7, 0x60, 0x00, 0x00, 0xF8, 0x75, 0xAC, 0x12 | Returns TRUE if the device hardware supports General MIDI |
| Sample memory size | 0x178F2F28, 0xC364, 0x11D1, 0xA7, 0x60, 0x00, 0x00, 0xF8, 0x75, 0xAC, 0x12 | Returns the amount of available memory in the device in samples |
| Sample playback rate | 0x2A91F713, 0xA4BF, 0x11D2, 0xBB, 0xDF, 0x0, 0x60, 0x8, 0x33, 0xDB, 0xD8 | Returns the sample playback rate in Hertz |
See also:
Downloadable Sounds (DLS) format
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